Hybrid Cysts Research Articles

Cutaneous hybrid cysts with matrical differentiation are mostly sporadic and related to CTNNB1 mutation.

Recurrent mutations in the CTNNB1 or APC genes leading to the activation of the Wnt/betacatenin pathway are observed in adnexal tumors with matrical differentiation. While most pilomatricomas arise sporadically and harbor CTNNB1 mutations, cutaneous hybrid cysts combining epidermal and matrical differentiations have been mostly reported in a context of the familial adenomatosis polyposis/Gardner's syndrome related to germinal mutations of APC. The objective of this study is to understand the pathogenesis of hybrid cysts combining epidermal and matrical differentiations. The 287 cases diagnosed as pilomatricoma/hybrid cysts registered between January 1, 2015 and February 21, 2023 in the Pathology Department at Tours University Hospital Center were considered for inclusion. After diagnosis confirmation, all cases were classified as pilomatricomas or hybrid cysts. Clinical data and microscopic features of the two groups were compared. Immunohistochemical detection of the betacatenin and CTNNB1/APC genes sequencing were performed in all hybrid cysts. Among the cohort, ten cases were classified as hybrid cysts (4%). None had a personal or familial history of familial adenomatosis polyposis. The immunochemistry confirmed a betacatenin nuclear expression in the matrical component in allexcepted one cases, while no nuclear accumulation was observed in the epidermal component of most hybrid cysts (n = 8, 80%). CTNNB1 mutations were detected in all hybrid cysts with interpretable sequencing data (n = 7/10). By contrast, only a variant of uncertain significance (class 3) was detected in APC in association with a pathogenic CTNNB1 mutation in one case. Hybrid cysts are rare entities consisting in 4% of the tumors analyzed in our study. Our results suggest that most hybrid cysts occur sporadically and are associated with CTNNB1 somatic mutations.

Clinicopathological Appraisal of Cutaneous Cysts: A 2-Year Retrospective Observational Study

Background: Cysts, primarily epidermal and trichilemmal, are commonly seen in clinical practice. Rupture, infection, inflammation, and rarely malignant transformation may complicate the cysts. This study aims to analyze the clinicohistological features of cutaneous cysts. Materials and Methods: A retrospective review of patients with the diagnosis of cyst confirmed on histopathology over the past two years (2020–2021) was performed. Clinical details comprised of age, gender, site of involvement, size, duration, and associated symptoms. Histological examination included cyst wall lining, type of keratinization, complications like rupture, inflammation, foreign body giant cell reaction, calcification, and malignant change. Results: A total of 324 cases with mean age of 37.9 years and equal gender distribution were identified. Most frequent diagnosis was epidermal cyst in 89.8%, followed by trichilemmal cyst in 8.9% of cases. Rare types included follicular hybrid cyst, verrucous cyst, vellus hair cyst, and steatocystoma. Most common complication was cyst rupture in 54.3% of epidermal cysts. Proliferating epidermal and proliferating trichilemmal cysts were noted in one and two cases, respectively. Two cases revealed malignancy arising in the wall of epidermal cyst. Limitations: The retrospective study design and non-availability of follow-up data, especially for proliferating cysts and cysts with malignant transformation were the main limitations of this study. Conclusion: Histopathologic examination of excised cutaneous cysts is paramount in reaching accurate diagnosis of the type of cyst and associated secondary changes to enable appropriate management.

Benign Cutaneous Cysts: A Comprehensive Analysis of 1160 cases.

Background Cysts are common skin abnormalities that are mostly benign; however, sometimes malignant lesions may present clinically as cystic manifestations. Benign cutaneous cysts can be of different morphological types and their diagnosis relies on histological evaluations. The most common mode of treatment is surgical excision, whichis curative. Methodology This is a retrospective cross-sectional study conducted at the Department of Histopathology, Chughtai Institute of Pathology, Lahore, Pakistan from 1st January 2020 to 31st December 2022. Non-probability consecutive sampling was done, and all the cases of benign cutaneous cysts were included. All cases were microscopically reviewed by two histopathologists, and variables like age, gender, site of the lesion, and histological diagnosis were noted. The data were analyzed using IBMSPSSStatistics for Windows, Version 29 (Released 2022; IBM Corp., Armonk, New York, United States). Results A total of 1160 recorded cases of benign cutaneous cysts were included. Overall gender distribution revealed males (n=489, 42.1%) and females (n=671, 57.8%). The age range was 3 to 91 years with a mean age of 37.56 ± 16.05 years.The three most common cysts were epidermal inclusion cysts (74.3%), trichilemmal cysts (15.1%), and dermoid cysts (6.3%). Other cysts were uncommon includinghidrocystoma (1.9%), steatocystoma (0.3%), verrucous cysts (0.3%), comedones (0.6%), hybrid cysts (0.2%), milia (0.3%), and vellus hair cysts (0.2%). The most common site was back (23.5%) for epidermal inclusion cysts, scalp (74.4%) for trichilemmal cysts, and eye (33.8%) for dermoid cysts. Conclusion Benign cutaneous cysts have a broad morphological spectrum with a wide age range. Epidermal inclusion cysts, trichilemmal cysts, dermoid cysts, and hidrocystoma account for the four most common types. For each of the other cyst type, the prevalence was under 1%. Female gender predominated in epidermal inclusion cysts, trichilemmal cysts, and dermoid cysts while male gender was common in other cysts. Overall majority of the cysts presented in the head and neck area.

Spectrum of Hybrid Cysts and Their Clinical Significance.

A hybrid cyst is a cutaneous cyst combining different types of keratinization of those seen in the folliculo-sebaceous-apocrine unit. Previous reports found that it may be occasionally associated with Gardner syndrome. This study aimed to clarify the pathologic findings and clinical significance of hybrid cyst based on case series observations. We retrospectively reviewed patients who fulfilled the pathological criteria of hybrid cyst from 2001 to 2015. The patient profiles, clinical presentations, pathological findings, and associated diseases were analyzed by reviewing the medical records and slides. A total of 71 hybrid cysts were confirmed over the study period. There were 12 pathologic variants. The most frequent variant was combined infundibular cyst and tricholemmal cyst (22 in 71 cases, 30%), followed by infundibular cyst and pilomatricoma (14 in 71 cases, 19%). There was no significant association between sex, age, or site and the pathological type of hybrid cyst. Neither extra-intestinal manifestation nor a family history of Gardner syndrome was found in any case. Hybrid cysts could contain a variety of combinations of components from the folliculo-sebaceous-apocrine unit. No clinical significance was found between demographics and the type of hybrid cyst. No association with Gardner syndrome was identified in this case series.

Multiple Hybrid Cysts in a Child: Challenge.

Multiple Hybrid Cysts in a Child: Challenge.

In situ carcinoma in a hybrid cyst: a case report

Follicular hybrid cysts including two or more components of the epithelial skin adnexa are very rare. The epithelial lining of hybrid cysts varies, and either contains epidermis, and trichilemmal squamous epithelium, or other epithelia of the skin adnexa. Hybrid cysts may also be associated with neoplasia, such as in situ carcinoma, Bowen's disease and squamous cell carcinoma. A 37-year-old female was complaining of a cyst on her scalp. The unilocular cystic lesion was lined with markedly atypical squamous cells with trichilemmal differentiation. Marked nuclear and cytological atypia, pleomorphism, numerous mitotic figures and atypical mitosis was detected in the squamous epithelium. The epithelium of the cyst was also composed of ductal structures lined with cuboidal epithelium. Immunohistochemical staining was positive for cytokeratin 7 (CK7) in both squamous and glandular epithelium. Luminal staining was shown by carcinoembryonic antigen (CEA), although gross cystic disease fluid protein-15 (GCDFP-15) was negative in the glandular epithelium. In addition, p16 tumor suppressor gene was strongly positive in both the squamous and glandular epithelium. Overall, the unique cystic lesion reported contained pilar squamous epithelium with in situ carcinoma and eccrine ductal structures, which was interpreted as a hybrid cyst composed of in situ trichilemmal carcinoma and a ductal eccrine component.

Basal Cell Carcinoma Arising from a Follicular Hybrid Cyst

Malignant tumors arising from follicular cysts are rare. Herein, we report of a 62-year-old Japanese woman with a slowly growing tumor, 22 × 20 mm in size, located on her nose for 2 years. Histopathological examination of the surgically excised tumor showed that the tumor cells were basaloid and formed peripheral palisading patterns. The tumor contained a cystic structure in its center, and the cyst wall was lined with stratified epithelium with or without keratohyalin granules. Based on these findings, a diagnosis of basal cell carcinoma arising from a follicular hybrid cyst was made. To our knowledge, this is the first case of basal cell carcinoma originating from a follicular hybrid cyst. A review of previous reports of basal cell carcinoma from a follicular cyst indicated that the majority of previous cysts were located on the face, and that the lesions had been present for a relatively long time. The present case showed typical clinical findings and followed a regular course. Malignant transformation may be a rare event, but it can occur in a follicular cyst, so cysts and suspected cysts, especially those found on the face and those persisting for relatively long time, should always be subjected to histological examination.

Histologic and Immunohistochemical Characteristics of Cutaneous Cysts in Goltz–Gorlin Syndrome

Goltz-Gorlin syndrome presents with multiple basal cell carcinomas, odontogenic keratocysts, and cutaneous cysts, among other manifestations. The cutaneous cysts have been described as both epidermoid cysts and keratocysts but were not further characterized. Light microscopic examinations were made on 23 cutaneous cysts in 4 patients associated with Goltz-Gorlin syndrome located on extremities, face, trunk, palms, and soles and compared with nonsyndromic vellus hair cysts, steatocystomas, and hybrid cysts. Twenty-one of the syndromic cysts revealed alternating infundibular-like and steatocystoma-like squamous epitheliums in varying proportions. The cysts were lined by both smooth and corrugated squamous epithelium. The horny layer was composed by alternating areas of thin, lamellate, and compact eosinophilic keratin. Only 2 cases showed an exclusive steatocystoma-like type of epithelium very similar to odontogenic keratocysts. Sebaceous glands and follicular structures were absent. There were no differences between palmar and plantar cysts and other anatomic locations. The ultrastructural findings in syndromatic cysts confirmed variable expression of keratohyalin granules. Only 3 of 6 cases of nonsyndromic hybrid cysts showed overlapping features with syndromic cysts. Immunohistochemical profiling of keratin, involucrin, filaggrin, loricrin, and BCL-2 expression in syndromatic cysts showed exclusive positivity of K19 and continuous staining for BCL-2. In summary, 2 types of cutaneous cysts are characteristic of Goltz-Gorlin, irrelevant of their anatomic location, namely steatocystoma-like and more frequently hybrid-like. The diagnosis of syndromic hybrid-like cysts should be considered whenever infundibular and steatocystoma differentiation alternate and overlap. Altogether, these findings in epithelial cysts may raise the suspicion of Goltz-Gorlin as an underlying cause.

Follicular Hybrid Cyst With Isthmic-Catagen, Pilomatrical, and Syringocystadenoma Papilliferum Components

Follicular Hybrid Cyst With Isthmic-Catagen, Pilomatrical, and Syringocystadenoma Papilliferum Components

Immunohistochemical Study of Calretinin in Normal Skin and Cutaneous Adnexal Proliferations

Calretinin is a calcium-binding protein member of the EF-hand family. The presence of calretinin has been demonstrated in certain stages of the cellular cycle in a wide variety of normal and neoplastic tissues. The main aims of our study were (1) to investigate what structures of the normal skin and cutaneous adnexal proliferations express immunoreactivity for calretinin and (2) to determine the value of immunohistochemical expression for calretinin as a marker for follicular, sebaceous, apocrine, and eccrine differentiation in cutaneous adnexal proliferations. We studied 139 biopsy specimens, including 10 cases of normal skin of different locations and 129 benign and malignant cutaneous adnexal proliferations. In normal skin, we found that calretinin is expressed in the innermost cell layer of the outer root sheath in anagen hair follicle, in both the duct and sebolemma of the sebaceous gland, in the secretory portion of eccrine glands, and in mast cells of the stroma. In cutaneous adnexal proliferations, we found strong immunoreactivity for calretinin in tricholemmal cysts, tricholemmomas/inverted follicular keratoses, tumors of follicular infundibulum, and in some basal cell carcinomas. Focal positivity was also seen in trichoadenomas, trichoblastomas/trichoepitheliomas, pilomatricomas, proliferating tricholemmal tumors, pilar sheath acanthomas, trichofolliculomas, follicular hybrid cysts, cutaneous mixed tumors, steatocystomas, sebaceous hyperplasias, and sebaceomas. These results demonstrate that immunohistochemical study for calretinin may be helpful to identify the innermost cell layer of the outer root sheath in anagen hair follicle and the cutaneous adnexal proliferations showing differentiation toward this structure. Calretinin immunoreactivity supports eccrine differentiation in some sweat gland neoplasms, and it is also useful in identifying neoplasms with ductal sebaceous differentiation.

Follicular hybrid cyst on the cheek: A combination of infundibular, isthmic, and pilomatrical differentiation

A hybrid cyst is a rare condition which includes any type of cyst arising from the various parts of the pilosebaceous unit. We report a case of hybrid cyst with infundibular, isthmic, and pilomatrical differentiation. A 12-year-old boy presented with a mass on the right cheek. The physical examination revealed an oval-shaped, dark-gray protruding mass with dimensions of 0.9 cm×0.6 cm that was non-tender to palpation. The mass was totally excised. The diagnosis of a hybrid cyst was confirmed by histological evaluation. It was a well-encapsulated mass and showed combined histologic features of infundibular, isthmus, and pilomatrical differentiation. The hybrid cyst is a follicular cyst that includes two or more components of a cystic lesion arising from the pilosebaceous unit. Occasionally, there have been reports of hybrid cysts consisting of two components in differentiation, but those showing more than two components of differentiation have been extremely rare. The pathogenesis of this unusual disease is not yet known.

Cutaneous Hybrid Cyst in a Sprague-Dawley Rat

This report describes a spontaneous hybrid cyst in a Sprague-Dawley (SD) rat. A 52-week-old, male SD rat had a cutaneous cyst on the left mystacial pad. Histologically, the cyst wall showed infundibular differentiation with keratohyalin granules in the granular layer and matrical differentiation comprising basaloid epithelial cells with trichohyalin granules. The cyst cavity was filled with lamellar, flaky keratin and aggregates of shadow cells. Immunohistochemically, the infundibular-type epithelium was positive for cytokeratin (CK) AE1/AE3, CK KL1 and CK14 but negative for CK15, whereas the matrical-type epithelium was negative for all four CK isoforms examined. These immunohistochemical properties of the infundibular- and matrical-type epithelia were similar to those of the infundibulum and inferior segment of normal hair follicles, respectively. Based on these findings, the cyst was diagnosed as a hybrid cyst, comprising more than one type of cyst arising from various parts of the pilosebaceous unit.

Paternal leakage of mitochondrial DNA in experimental crosses of populations of the potato cyst nematode Globodera pallida

Animal mtDNA is typically assumed to be maternally inherited. Paternal mtDNA has been shown to be excluded from entering the egg or eliminated post-fertilization in several animals. However, in the contact zones of hybridizing species and populations, the reproductive barriers between hybridizing organisms may not be as efficient at preventing paternal mtDNA inheritance, resulting in paternal leakage. We assessed paternal mtDNA leakage in experimental crosses of populations of a cyst-forming nematode, Globodera pallida. A UK population, Lindley, was crossed with two South American populations, P5A and P4A. Hybridization of these populations was supported by evidence of nuclear DNA from both the maternal and paternal populations in the progeny. To assess paternal mtDNA leakage, a ~3.4kb non-coding mtDNA region was analyzed in the parental populations and in the progeny. Paternal mtDNA was evident in the progeny of both crosses involving populations P5A and P4A. Further, paternal mtDNA replaced the maternal mtDNA in 22 and 40% of the hybrid cysts from these crosses, respectively. These results indicate that under appropriate conditions, paternal leakage occurs in the mtDNA of parasitic nematodes, and supports the hypothesis that hybrid zones facilitate paternal leakage. Thus, assumptions of strictly maternal mtDNA inheritance may be frequently violated, particularly when divergent populations interbreed.

Hybrid cyst on the sole

Hybrid cyst on the sole

Multiple follicular cysts in four alpacas (Vicugna pacos)

Follicular cysts are non-neoplastic skin lesions lined by follicular epithelium. The pathogenesis of these lesions is unclear. Multiple follicular cysts occur sporadically in dogs, horses and humans and are common in sheep. Here we report multiple follicular cysts in four aged alpacas (Vicugna pacos). Based on their histological features, they are most consistent with hybrid cysts. This is the first report of multiple follicular cysts in alpacas.

Epidermal cyst with pilomatricoma (follicular hybrid cyst): Immunohistochemical study with epithelial keratins and filaggrin

The Journal of DermatologyVolume 37, Issue 10 p. 922-925 Epidermal cyst with pilomatricoma (follicular hybrid cyst): Immunohistochemical study with epithelial keratins and filaggrin Nanae TSUJI, Nanae TSUJI Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorIchiro KUROKAWA, Ichiro KUROKAWA Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorKazuya TOKIME, Kazuya TOKIME Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorYo-ichi OMOTO, Yo-ichi OMOTO Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorYuko SENBA, Yuko SENBA Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorKoji HABE, Koji HABE Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorKei-ichi YAMANAKA, Kei-ichi YAMANAKA Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorKen-ichi ISODA, Ken-ichi ISODA Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorAiro TSUBURA, Airo TSUBURA Department of Pathology, Kansai Medical University, Osaka, JapanSearch for more papers by this authorHitoshi MIZUTANI, Hitoshi MIZUTANI Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this author Nanae TSUJI, Nanae TSUJI Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorIchiro KUROKAWA, Ichiro KUROKAWA Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorKazuya TOKIME, Kazuya TOKIME Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorYo-ichi OMOTO, Yo-ichi OMOTO Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorYuko SENBA, Yuko SENBA Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorKoji HABE, Koji HABE Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorKei-ichi YAMANAKA, Kei-ichi YAMANAKA Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorKen-ichi ISODA, Ken-ichi ISODA Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this authorAiro TSUBURA, Airo TSUBURA Department of Pathology, Kansai Medical University, Osaka, JapanSearch for more papers by this authorHitoshi MIZUTANI, Hitoshi MIZUTANI Department of Dermatology, Mie University Graduate School of Medicine, Tsu, MieSearch for more papers by this author First published: 23 September 2010 https://doi.org/10.1111/j.1346-8138.2010.00905.xCitations: 2 Ichiro Kurokawa, M.D., Department of Dermatology, Mie University Graduate School of Medicine, 2-174 Edobashi, Tsu, Mie 514-8507, Japan. Email: kuroichi@clin.medic.mie-u.ac.jp Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume37, Issue10October 2010Pages 922-925 RelatedInformation

Hybrid cysts: A clinicopathological study of seven cases

Hybrid cysts develop from more than two components of the pilosebaceous unit. The pathogenesis of this unusual disease has not yet been elucidated. The aim of this study was to assess the clinical and histopathological features of hybrid cysts. Histological sections of seven cases indexed as hybrid cysts were reviewed from 1996-2009 at the Department of Dermatology, Eulji Medical Center, Seoul, Korea. Hospital charts and slides were retrospectively evaluated. All cases had a combination of an epidermal cyst and a pilomatricoma with sharp transitional zones. The epidermal cyst lining was composed of thickened stratified squamous epithelium with a granular layer. Basophilic cells, shadow cells and the contents of the pilomatricoma were present in all lesions. There were no differences in the clinical features between patients with hybrid cysts and others with single cystic lesions. There were five women and two men, ranging in age from 11 to 50 years (mean 27 years). The most common sites were the upper extremities. None of the patients had any sign of Gardner's syndrome. Hybrid cysts are an interesting pathological phenomenon. Further study is needed to analyze hybrid cysts to improve our understanding of their pathogenesis and development from tumours of the pilosebaceous unit.

Outbreeding lethality between toxic Group I and nontoxic Group III Alexandrium tamarense spp. isolates: Predominance of heterotypic encystment and implications for mating interactions and biogeography.

We report the zygotic encystment of geographically dispersed isolates in the dinoflagellate species complex Alexandrium tamarense, in particular, successful mating of toxic Group I and nontoxic Group III isolates. However, hypnozygotes produced in Group I/III co-cultures complete no more than three divisions after germinating. Previous reports have suggested a mate recognition mechanism whereby hypnozygotes produced in co-cultures could arise from either homotypic (inbred) or heterotypic (outbred) gamete pairs. To determine the extent to which each occurs, a nested PCR assay was developed to determine parentage of individual hypnozygotes. The vast majority of hypnozygotes from pairwise Group I/III co-cultures were outbred, so that inviability was a result of hybridization, not inbreeding. These findings support the assertion that complete speciation underlies the phylogenetic structure of the Alexandrium tamarense species complex. Additionally, the ribosomal DNA (rDNA) copy numbers of both hybrid and single ribotype hypnozygotes were reduced substantially from those of haploid motile cells. The destruction of rDNA loci may be crucial for the successful mating of genetically distant conjugants and appears integral to the process of encystment. The inviability of Group I/III hybrids is important for public health because the presence of hybrid cysts may indicate ongoing displacement of a nontoxic population by a toxic one (or vice versa). Hybrid inviability also suggests a bloom control strategy whereby persistent, toxic Group I blooms could be mitigated by introduction of nontoxic Group III cells. The potential for hybridization in nature was investigated by applying the nested PCR assay to hypnozygotes from Belfast Lough, Northern Ireland, a region where Group I and III populations co-occur. Two hybrid cysts were identified in 14 successful assays, demonstrating that Group I and III populations do interbreed in that region. However, an analysis of mating data collected over an 18-year period indicated a leaky pre-mating barrier between ribosomal species (including Groups I and III). Whether the observed selectivity inhibits hybridization in nature is dependent on its mechanism. If the point of selectivity is the induction of gametogenesis, dissimilar ribotypes could interbreed freely, promoting displacement in cases where hybridization is lethal. If instead, selectivity occurs during the adhesion of gamete pairs, it could enable stable coexistence of A. tamarense species. In either case, hybrid inviability may impose a significant obstacle to range expansion. The nested PCR assay developed here is a valuable tool for investigation of interspecies hybridization and its consequences for the global biogeography of these important organisms.

Hybrid Cysts of the Eyelid With Follicular and Apocrine Differentiation: An Under-recognized Entity?

To describe 6 patients with hybrid cysts of the eyelid that demonstrated follicular and apocrine differentiation. Clinicopathologic series of 6 cases obtained from review of 1,099 cases of hidrocystoma diagnosed at the New York Eye and Ear Infirmary from 1990 to 2006. Six patients, aged 38 years to 85 years (mean 66.5 years), was examined for cystic eyelid lesions. Histopathologic evaluation revealed cystic structures, lined by a combination of apocrine, infundibular (epidermoid), and trichilemmal-type epithelia. Luminal contents consisted of variable amounts of lamellated and compact keratin, and serous material. Contiguity with a hair follicle was demonstrated in 4 of 6 lesions. Immunohistochemical evaluation showed intense immunoreactivity of the entire cyst lining in all lesions for high molecular weight cytokeratin and variable immunoreactivity for low molecular weight cytokeratin. All cystic structures displayed immunoreactivity for carcinoembryonic antigen. Weak focal immunoreactivity for S-100 protein and gross cystic disease fluid protein-15 was observed in most lesions. Hybrid cysts can show apocrine, trichilemmal, and infundibular differentiation, suggestive of their origin at the junction of keratinizing squamous and glandular epithelia of the hair follicle. Although, to our knowledge, only 1 such lesion has been described in the eyelid skin, it is likely that hybrid cysts of the eyelid are not an infrequent finding.

A Case of a Follicular Hybrid Cyst

Various cutaneous cysts such as epidermal cysts, trichilemmal cysts, vellus hair cysts, steatocystoma, or pilomatricoma can arise from a different part of the pilosebaceous unit, namely the infundibulum, isthmus, sebaceous ducts, and bulbar or inferior portion. Rarely, a hybrid cyst that includes two or more components of a cystic lesion arising from the pilosebaceous unit can develop. The pathogenesis of this unusual disease is not yet known. We report a case of a follicular hybrid cyst which showed combined histologic features of both an epidermal cyst and pilomatricoma, and discuss the possible pathomechanism of the development of this hybrid cyst with a review of the literature. (Ann Dermatol (Seoul) 19(4) 153~156, 2007)